This invention relates to a measurement system and method for probing dense, high pressure sprays and, more particularly, to a tomographic spray momentum mapping system, which utilizes a mechanical wire probe to obtain spray momentum measurements throughout the spray and a computed topography software program for processing and integrating these measurements for mapping the spray momentum distribution.
A compression-ignition (xe2x80x9cCIxe2x80x9d)engine, first developed for diesel fuel, is an engine that does not use a spark to ignite fuel. When air is compressed and fuel is injected into a CI engine, the fuel ignites. A direct-injection (xe2x80x9cDIxe2x80x9d)engine is an engine in which the fuel is injected by mechanical action into the combustion chamber. Compression-ignition, direct-injection (xe2x80x9cCIDIxe2x80x9d)engines are used predominantly in the trucking, rail and shipping industries.
The recent development of high-pressure, electronically-controlled injection systems has made it possible to improve CIDI engines to the point where they are suitable for use in passenger vehicles as well. The outstanding benefit of this type of engine is its very good fuel economy, which has the potential to significantly reduce the nation""s fuel use, as well as reducing the production of carbon dioxide by passenger vehicles. The drawbacks of CIDI engines are its high emissions, primarily nitrous oxides and particulates, for which satisfactory exhaust after-treatment does not yet exist.
In order to further improve the efficiency and to reduce emissions in CIDI engines, it is necessary to understand the fundamental physical processes that take place in the engine""s combustion chambers. Formation and destruction of pollutants are controlled to a great extent by the mixing process. In turn the efficiency of in-cylinder mixing is dependent upon the fuel spray created by the fuel injector. In order to reduce the amount of pollutants formed by the engine, it is advantageous to study the characteristics of the fuel spray structure. Fuel spray studies provide insight into the spray-gas mixing process and facilitate development and evaluation of new injection hardware and fuel injection strategies. Such analysis can also provide data for the development and improvement of computer models of the spray and its combustion.
Because of the lack of experimental tools suitable for probing dense, high pressure fuel sprays, researchers currently lack information necessary for the improvement of engine performance. Thus, the present tomographic spray momentum mapping system has been developed to provide researchers with a practical tool suitable for probing dense, high pressure fuel sprays.
The ability to measure momentum distributions in sprays will be of even greater importance in the future if new fuels such as dimethyl-ether or xe2x80x9cbio-dieselxe2x80x9d fuel gain importance. These fuels generally have physical properties such as viscosity and distillation curves significantly different from those of current fuels. These fuels can markedly change the characteristics of fuel spray and have a substantial effect on combustion quality. Further, it may be necessary to modify fuel injection hardware in order to exploit these fuels making accurate analysis of fuel spray characteristics critical to engine and injection system manufacturers.
Currently, sprays are primarily studied using optical techniques such as direct imaging and laser Doppler velocimetry. Direct imaging techniques provide information on physical characteristics such as spray penetration, spray angle, the initial dispersion angle of the nozzle, initial spray tip speeds, and total momentum measurement. Doppler velocimetry techniques provide information regarding particle velocity, particle size, spray angle variations and spray asymmetry.
However, because of the high density of diesel sprays, the information obtained by optical techniques is necessarily limited to that which may be obtained in the outer envelope of the spray. These techniques do not provide critical information such as velocity, mass, and droplet size distribution within the spray and, more particularly, near the fuel injector nozzle. A further limitation of optical techniques is that only thin sprays can be studied due to the need for optical transparency of the sprays. In contrast the use of the mechanical spray probe of the present system eliminates the need for optical transparency, and even the interior portions of dense fuel sprays may be investigated.
One example of a prior art method of measuring fluid streams is shown in U.S. Pat. No. 3,338,093 to Usry et al. which discloses a device for measuring the momentum and solidity of fluid free streams from injection valves by causing a wire of generally triangular cross-section to transect the stream in such a manner that the stream impinges on the base of the triangle measuring the position of the wire and the force of the fluid impinging on the wire.
Another example of prior art spray analysis is shown in U.S. Pat. No. 2,756,591 to Hagerty et al. which discloses a spray analyzer that has a probe to be positioned in the spray and that provides a permanent record of the spray performance in the form of a chart reading mass distribution or momentum changes along the ordinate and angular displacement around the circle of a round or conical spray along the abscissa of the chart.
Another example of a prior art spray analysis is illustrated in U.S. Pat. No. 3,449,948 to Willowick et al. which discloses a nozzle spray test device for determining spray cone vertex angle of fuel injection nozzles. In this device the injection nozzle to be tested is clamped in the test device and connected to a fuel pressure source, the conical fuel spray issuing from the nozzle being directed into a chamber having aligned detectors or probes which are adjustable radially inwardly or outwardly to be impinged by elements of the conical fuel spray.
Another example of a prior art device for spray analysis is shown in U.S. Pat. No. 5,753,806 to Ryan et al. which discloses an apparatus and method for determining the distribution and flow rate characteristics of an injection nozzle wherein a plurality of piezoelectric sensors are disposed in a spatial array around the ports of an injection nozzle. Separate electrical signals proportional to the instantaneous momentum of fluid discharged from the injection nozzle and impacting on each of the sensors are used to calculate the instantaneous momentum and mass flow rate of fluid impacting each of the sensors.
Another example of prior art spray analysis is disclosed in U.S. Pat. No. 5,686,989 to Hoffinan et al. which shows a transient spray patternator. This device utilizes a honeycomb structure to collect the spray in individual tubes positioned through a given cross-section of the spray permitting measurement of the mass flux distribution, penetration rates, droplet sizing and distribution within either a steady state or transient spray pattern.
Another example of prior art fluid flow analysis is shown in U.S. Pat. No. 5,663,508 to Sparks which discloses a silicon flow sensor wherein the primary sensing component is preferably formed by a single silicon chip on which associated signal conditioning and compensating circuitry can be provided. The flow sensor is intended for purposes such as determining the flow rate of intake air to an automotive engine.
Another example of prior art fluid flow analysis is illustrated in U.S. Pat. No. 5,120,951 to Small which discloses an optoelectronic motion and fluid flow sensor wherein a resilient member is fixedly supported at one end thereof and entrained in the fluid for varying the amount of light incident on the photosensor from the light source as a function of the amount of deflection of the resilient member caused by motion of the fluid in a passageway.
Another example of prior art fluid flow analysis is shown in U.S. Pat. No. 4,920,808 to Sommer which discloses a device and method for measuring the flow velocity of a free flow in three dimensions in the case of strongly fluctuating incident flow directions such that the flow measuring device is aligned in the flow by means of a servo-mechanism in such a way that its central axis extends in the direction of flow, the pressure being measured at several points on the front spherical cap thereof.
Another example of a prior art flow measuring system is described in U.S. Pat. No. 4,715,232 to Buettner which discloses a flow measuring system employing a manometer and a pilot rod having at least two orifices and wherein upset or temporary inversion of the manometer will not result in backflow of any indicating liquid into the primary liquid carrying pipeline.
Another example of a prior art fluid measuring system is shown in U.S. Pat. No. 4,648,278 to Lew which discloses a spiral coil target flowmeter employing a spiral coil target coaxially disposed within a flow passage included in the body of the flowmeter wherein the drag and/or torque imposed on the spiral core target by the moving fluid medium is measured and converted to the flow rate of the fluid medium moving through the flow passage.
Another example of a prior art fluid flow device is illustrated in U.S. Pat. No. 4,397,190 to Hulin which discloses an apparatus and method for determining flow characteristics of a polyphase fluid flowing in a conduit wherein two differential pressure sensors are provided, each having two pressure ports sensitive to local pressure variation in the fluid. The pressure ports are maintained in a predetermined spatial relationship and in a predetermined orientation relative to the general direction of the flow.
Another example of a prior art fluid flow measurement method is shown in U.S. Pat. No. 4,317,178 to Head which discloses a method and systems for conducting a multiple velocity traverse of a flow stream cross section of a known shape and area to determine flow therethrough.
Another example of prior art fluid flow measurement is described in U.S. Pat. No. 5,003,810 to Jepson et al. which discloses a fluid meter comprising at least three sensors each having an output dependent on a respective characteristic of the fluid to be monitored, circuitry to combine the outputs of two of the sensors to provide a measurement of mass flowrate of the fluid, and to combine the outputs of the three sensors to provide an error signal which can be used to recalbrate the measurement.
Another example of prior art fuel spray testing is shown in U.S. Pat. No. 4,165,635 to Komaroff et al. which discloses a method of testing fuel-injector spray nozzles with respect to proper buzzing and seal tightness wherein a laser beam is directed onto a light detector along a path passing close to the spray orifice(s) of a fuel-injection spray nozzle.
Another example of prior art spray pattern measurement is shown in U.S. Pat. No. 3,459,049 to Kamps wherein a pattern separator in the form of flow dividing partitions is placed in spaced proximity to a nozzle or spray head and the fluid emerging from the nozzle is collected, identified with the orifices in the several nozzle areas, and lead off to a series of individual measuring devices also identified with the several spray head areas.
The use of a probe to measure both the total momentum and the momentum at a single point in the spray is disclosed in a German publication, Messung der Strahlkraft und-bewegungsgrxc3x6sse zur Beurteilung der Zerstxc3xa4ubungsgxc3xcte von Einspritzstrahlen, by Iwan Komoroff und Kurt Melcher, Bosch Techn. Berichte 3xe2x80x94Heft 6xe2x80x94Dezember 1971 and cited herein. Komoroff and Melcher measured the momentum of a spray by using a circular plate attached to a force transducer. In this device the circular plate may be larger than the spray diameter to measure the total spray momentum, or small enough to sample only a small portion of the spray. However, this type of mechanical probe has inherent disadvantages in that it strongly perturbs the spray, its resolution is insufficient for making spatially-resolved measurements near the nozzle, and the signal obtained from a probe with reasonable spatial resolution is very weak.
A technical advance is achieved in the present invention by the use of a minimally intrusive, fine gauge, wire probe integrated with a force transducer, which is traversed through the spray in a plane perpendicular to its geometric axis. The spray impinges on the wire probe to produce force measurements, which are input to a computed topography software program in a computer. Computed topography (CT) is an imaging technique that uses an array of detectors or measurements to collect information from an object. The information or data collected is utilized by a computer to reconstruct the structure of the object, and the resulting image can be displayed, for example, on a computer screen.
Computed topography was first used about 35 years ago to xe2x80x9creconstructxe2x80x9d the density distribution in a patient""s body from measurements of the attenuation, of x-ray radiation passed through it. Since that time CT has been used by researchers in the, physical sciences and engineering for applications in which only integral (as opposed to pointwise) measurements are available. Computed topography techniques make it possible to convert these integrated measurements into a map giving the quantity of interest at each point in a 2- or 3-dimensional domain.
Advantageously, the tomographic spray momentum mapping system of the present invention provides a innovative tool for probing dense, high-pressure sprays by using integrated measurements combined with tomographic data processing to reconstruct spray momentum distributions for analysis.
Accordingly, the present invention provides a tomographic spray momentum mapping system and method suitable for probing and determining the spray momentum at all points of dense, high pressure sprays. It is based on a minimally-intrusive, mechanical probe, which is traversed through the spray to obtain momentum measurements at selected points throughout the spray. The present method utilizes computed topography techniques to convert these measurements into a map giving the spray momentum in a two or three-dimensional domain.
The spray probe assembly consists of a fine gauge wire stretched and held in a Y-shaped yoke or handle. The wire is traversed through the spray in a plane perpendicular to the geometric axis of the spray. An energy-transforming transducer attached in operative relation to the yoke receives a force input from the impact of the spray with the probe wire and generates output measurements, which are proportional to the integrated total force exerted by the spray on the wire.
The output measurements derived from the transducer are electronically conditioned and input to a computer system. In the computer, a tomographic software program processes the force measurements to provide the spray momentum at all points in the spray. This information may be used directly for understanding spray structure and improvement of injection systems, and indirectly for improvement of computer spray models used to simulate engine performance.
Other features and advantages of the present invention will become apparent from a study of the following description and the accompanying drawings.